1. Field of the Invention
The present invention relates to a semiconductor package and a method for fabricating the same, and more particularly, to a semiconductor package including a thermal interface material (TIM) and a method for fabricating the same.
2. Description of the Related Art
It is essential for semiconductor packages for microprocessors and power semiconductor modules to transfer the heat generated during their operation sufficiently to the outside to prevent the degradation of the semiconductor chips.
For this purpose, a thermal interface material (TIM) is typically installed between a semiconductor chip and a lid or between a lid and a heat sink in a semiconductor package. A phase change material (PCM), which is one of the TIM, has excellent heat conductivity and interfacial adhesive strength. The PCM, however, has a defect in that it changes into a liquid state at a high temperature, e.g., above 60° C. That is, the PCM melts and does not function as the TIM at a high temperature, thereby deteriorating the performance of semiconductor packages.
FIG. 1 is a cross-sectional view of the structure of a TIM of a conventional semiconductor package. Referring to FIG. 1, a semiconductor chip 20 is attached to a substrate 10 via bumps 30, and a TIM 40, which is a PCM, is formed on the semiconductor chip 20. Then, a lid 50 is attached to the substrate 10 via a sealant 60, thus encapsulating the semiconductor chip 20. The TIM 40 transmits heat generated from the semiconductor chip 20 to the lid 50, and vice versa because it maintains a solid shape below a predetermined temperature. However, at high temperatures, the TIM 40 is liquefied and then flows away from the original position of the TIM 40. Thus, the TIM 40 loses its inherent functions such as heat conductivity and interfacial adhesive strength.
FIG. 2 includes plan views for explaining changes in the shape of the TIM 40 when a temperature cycling test is performed on a conventional semiconductor package. Referring to FIG. 2, the temperature cycling test is one of many reliability tests that test how much a semiconductor package deteriorates due to heat by repeatedly placing the semiconductor packages at −55° C. and 125° C. for a predetermined time, respectively.
FIG. 2 includes, on the left side, a plan view of a semiconductor package prior to performing the temperature cycling test thereon, taken by an ultra-sonograph. Here, it should be noted that there is no change in the shape of the TIM 40 disposed between the semiconductor chip 20 and the lid 50.
On the center of FIG. 2 is shown a plan view of the semiconductor package on which the temperature cycling test (during which the semiconductor packages are placed at −55° C. and 125° C. for a predetermined time) was performed about 164 times. At this time, about 30% of the TIM 40 is liquefied and flows away.
On the right is shown a plan view of each of the semiconductor packages on which the temperature cycling test (during which the semiconductor packages are placed at −55° C. and 125° C. for a predetermined time) was performed about 773 times. At this time, only about 40% of the TIM 40 remains.